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Let the capacity of bottle A and the capacity of bottle B be \(x\left(ml\right)\), \(y\left(ml\right)\) respectively.

We can deduce simutaneous equations:

\(\left\{{}\begin{matrix}x+y=600\\0.15\times x+0.4\times y=0.3\times600\end{matrix}\right.\)

From the first equation, we have: (1)  \(y=600-x.\)

Substituting (1) to the secon equation we get: \(0.15\times x+0.4\times\left(600-x\right)=180.\).

We can easily find \(x=240.\)